PESTS OF CORN/SORGHUM

Extracted from INSECT and related PESTS of FIELD CROPS (AG-271)
Dated 5/82
Placed on the Web 6/95 by the Center for Integrated Pest Management, NCSU

In 1980, corn was planted on 708,502 hectares (1,750,000 acres) of
North Carolina farm land concentrated in the Coastal Plain, but
also scattered throughout the Piedmont and Mountains. Grain sorghum
accounted for an additional 46,559 hectares (115,000 acres) in the
Piedmont and south central counties of this state. The corn and
sorghum planted on this extensive acreage are subject to
infestation by a diverse array of insect or related pests.

Although these two crops are unlike in many respects, (e.g.,
sorghum being much more drought tolerant than corn), they have many
pests in common. When present, many of these pests go unnoticed
because they are hidden within the soil, stalk, ear, seedhead, or
whorl. Few corn and sorghum pests feed on exposed sites where they
can be easily detected and controlled before damage occurs. As a
result, much attention needs to be focused on early recognition of
both pests and their injury so control measures may be employed at
the most appropriate time.

Key to Pests of Corn and Sorghum

A. Insects that feed on seed, roots, lower stems, or surface
debris.

Beetles - These chewing insects have hard, shell-like forewings (wing covers or elytra) which meet in a straight
line down the middle of the back (Fig. A, B). They may or may not
be able to fly.

Billbugs -
These black, gray, or brown
snout beetles are 10 to 16 mm long (Fig. A). They pierce young
seedlings near the ground with their "beak," causing stunting, tip
dieback, and often death of corn seedlings. Plants which survive
display yellow streaks, suckering, and rows of holes transverse
across the blades.

Sugarcane beetle -
This black, hardshelled,
dome-shaped beetle (Fig. B) is about 13 mm long. As it feeds
below the ground line on the lower stalks of corn seedlings, a
large ragged hole is left in the stalk. Damage is most common in
corn following sod.

Beetle larvae - These larvae are either legless or
have three pairs of short legs near the head (Fig. A to D).

Billbug larvae -
Several species of these
cream-colored, brown-headed, legless grubs (Fig. A) tunnel in the
basal area of the stalk, dwarfing and often killing plants.
Billbug larvae range from 2 to 15 mm long.

Southern corn rootworm
- This wrinkled,
yellowish-white larva (Fig. B) has three pairs of short legs and
measures 15 to 16 mm long when mature. The last segment of the
body has a brown, dorsal shield.

White grubs -
These C-shaped, brown-headed
grubs (Fig. C) may be as long as 45 mm, and have three pairs of
legs and a slightly enlarged abdomen. They feed heavily on roots of
grass crops, stunting and sometimes killing plants.

Wireworms - Injury by these slender, short-legged
larvae (Fig. D) produces stunting, tip dieback, and
chlorotic blades. Taproots of recently infested plants usually
display an irregular feeding hole with jelly-like plant secretions.
Damage to germinating corn is common. Larvae of most species are
cream to copper in color.

Melanotus communis
- This pale
yellow to reddish-tan wireworm is 21 to 25 mm long, and its last
abdominal segment has blunt scalloped edges (Fig. A). This pest
usually feeds on the roots of seedlings. Older infested plants are
stunted and may not tassle.

Southern potato
wireworm - This
white, cream, or yellow-gray larva has a red-orange head capsule
and may be as long as 17 mm. The last abdominal segment terminates
in a closed, oval notch (Fig. B).

Tobacco wireworm
- This brown-headed,
white, yellowish or cream-colored wireworm, 14 to 19 mm
long when mature, is characterized by a V-shaped notch in its last
abdominal segment (Fig. C).

Corn root aphid - This
typically wingless, pale
green to blue-green aphid has a black head and black or
reddish eyes. Some females are gray and pink with a white, powdery
coating. Length varies from 0.3 mm for small nymphs to 2.0 mm for
mature adults. Usually associated with anthills in corn fields,
this aphid feeds on the roots causing the foliage to develop a
yellowish to reddish tinge.

Caterpillars - These moth larvae have three pairs
of legs near the head and five pairs of prolegs.

Cutworms - These fat, darkly colored
caterpillars burrow in soil and debris during the day and cut off
or partially sever seedlings near the soil line at night.

Black cutworm -
This caterpillar, 3.5
to 45.5 mm in length, varies from light gray to black in color,
often appearing greasy. The skin of this cutworm is granulated (as
seen under a 10X hand lens), the granules resembling rounded,
flattened pebbles (Fig. A). After cutting off a seedling, this
cutworm commonly pulls it into the entrance of its burrow and feeds
on it during the day.

Granulate cutworm - This caterpillar,
2.0 to 38.5 mm long, has a pale brown head, a dark brown band down
its back, and brown sides with faint stripes. The skin granules of
this cutworm are like blunt cones as high as they are wide (Fig.
B).

Lesser cornstalk
borer - This larva may be
found feeding on leaves or roots but eventually tunnels into the
plant's stem usually at or near the soil line. A silken, soil-covered
tube is often connected to the plant stem at the entrance
hole. This small, slender, bluish-green caterpillar has brown bands
around each body segment and measures about 19 mm long when
mature.

Southern cornstalk
borer - This larvae,
which reaches a length of 25 mm, is creamy yellow during the winter
and white with black spots in the summer. Although it feeds in the
whorl early in its development, it later causes severe taproot and
lower stalk injury by tunneling within the plant.

Webworms (Sod Webworm,
Sorghum Webworm) - When mature, these pinkish-white,
yellow, or light-brown worms are 6 to 19 mm long with thick
bodies, coarse hairs, and paired dorsal and lateral spots on each
segment. They feed on the roots of seedlings, and bore into the
stalk near the soil line. Such stalk damage causes the plant to be
deformed and the newly emerged leaves to be ragged and distorted.
Fine silken strands entangled with plant debris are usually present
near the entrance hole.

Seedcorn maggot
- This tiny, legless, white to
yellow maggot is 5 to 7 mm long, tunnels in seeds and the
tender root tissue of seedlings. Many injured seeds do not
germinate and those which do produce weak, spindly seedlings which
rarely survive.

B. Small pests that extract juices from foliage and stems (Fig. A
to C).

Chinch bug
- This black bug, up to 4 mm long, has
opaque wings, each marked with a black triangle (Fig. A).
Feeding anywhere from the roots to the upper leaves, adults and
smaller, wingless, red and black nymphs cause dwarfing, lodging,
and yield reduction. Seedlings may wilt and die during severe
infestations.

Corn leaf aphid -
Up to 2 mm long, the wingless
form of this pear-shaped insect (Fig. 70B) is pale bluish-green
with a dark area around the base of the cornicles. Its body often
seems to have a powdery coating. The insects feed in groups of 5 to
over 2000. Tassels, leaves, and silks on which this aphid feeds
become black with mold. Leaf deformation, yellowing, and cast aphid
skins often are associated with heavy infestations.

Spider mites - Several
species of these eight-legged
(larvae six-legged), almost microscopic pests (Fig. 70C),
congregate and feed on the underside of leaves and spin webs on the
foliage. A silver speckling of the leaves, especially during dry
periods, is associated with these pests. In North Carolina, they
are usually a problem on corn rather than sorghum. Severe
infestations resemble drought stress since damage progresses from
the bottom of the plant up.

Carmine spider mite - The 0.4 mm long, oval
female is red, with two or four dark, dorsal spots; the male is
smaller and slightly diamond shaped.

Twospotted spider mite - The 0.4 mm long,
oval female is yellow dark green, with two or four dark, dorsal
spots; the male is smaller and diamond shaped. Webbing is initiated
near the midribs of the host plant and gradually envelopes the
plant as the population increases.

C. Caterpillars that bore into the whorl, stalk, or ear.
All larvae
described in this section have three pairs of legs near the head
and five pairs of prolegs.

green, reddish, or brown with pale, longitudinal stripes and
scattered black spots. Early instars are cream colored or
yellowish-green with few markings. Larval instars vary from 1.5 to
44 mm in length and have five pairs of prolegs. As injured leaves
unfurl, they display ragged holes and soggy, brown frass. This worm
also feeds on the tip kernels of the ear. Round emergence holes are
sometimes evident in the shuck.

caterpillar with a reddish-brown to black head reaches a length of
25.5 mm. Its boring into the stalk weakens the plant and causes
tassel and stalk breakage, ear dropping, and small ears. Light tan
frass entangled with silk, tunneled midribs, and pin holes in the
leaves indicate the presence of this pest.

-
This green, brown, or black worm
reaches a length of up to 40 mm and often has a pale, but distinct,
inverted "Y" on its head capsule (Fig. A). It has a black,
longitudinal stripe down each side of its body and a yellowish-gray
stripe down its back. It feeds in the whorl causing injury similar
to that of the corn earworm. It also attacks ears near the shank
and when mature may bore into the stalks. Unlike the corn earworm,
it rarely occurs in North Carolina before July.

Lesser cornstalk borer
- See section A.4.b.
for description. Especially during dry periods, this caterpillar bores
into the stalk within 5 cm of the soil surface leaving a soil-covered,
silken tube attached near the entrance site. Young injured
plants become distorted and fail to produce normal stalks and
ears.

Southern cornstalk borer - See section A.4.c.
for description. During early stages of development this larva feeds in
the whorl, causing emerging leaves to have rows of irregular holes
and sometimes damaging the growing point. Later it tunnels into the
stalk causing severe taproot and lower stalk injury.

Stalk borer - This caterpillar
may be solid white,
light purple, or cream colored with a dark brown band around the
middle and brown or purple longitudinal stripes. Reaching a length
of 31.8 mm, it may enter the stalk at ground level and sever leaves
as it moves upward or it may climb the plant and enter through the
bud and tightly coiled leaves. Tassels are usually destroyed and
the upper plant deformed. This insect is most common in no-till or
weedy fields.

D. Chewing insects that feed exposed on foliage or silks.

Armyworm -
This smooth-skinned, 30- to 35-mm long
caterpillar is basically yellowish or greenish brown with three
dark, longitudinal stripes and five pairs of prolegs.
The tan or greenish-brown head capsule has markings like those of
the fall armyworm, but on the armyworm, these markings are lighter
or less intense (Fig. B). Feeding primarily at night and spending
the days under ground litter, this insect may damage both tender
and mature foliage. In corn, this insect characteristically removes
foliage from the ground up, leaving only the midribs.

Beetles - These chewing insects have hard, shell-like
forewings (wing covers or elytra) which meet in a straight
line down the middle of the back when the beetles are not in flight
(Fig. A to C).

Corn flea beetle
- This oval, 1.3- to 2.5-mm
long insect (Fig. A) is about the size and shape of a #5
shotgun pellet. It chews the foliage of seedlings, leaving small
round holes and bleached-out spots or stripes. Basically black,
this beetle is tinged with bronze or bluish-green and usually jumps
very actively.

Japanese beetle
- This shiny, metallic
green, 13-mm long beetle has coppery brown wing covers (Fig. B).
It feeds on the silks of corn and in very severe infestations may
reduce pollination and kernel formation, although yield reduction
has not been documented in North Carolina.

Spotted cucumber
beetle - About 6-mm long,
this elongate, yellowish-green beetle has black legs, antennae, and
head as well as 12 black spots on its back (Fig. C). It feeds on
most above ground plant parts but causes greatest damage when it
severs newly emerged, unpollinated silks. As a result, ears of
corn are sparsely filled.

Grasshoppers
- Adults of various grasshopper
species, varying from 3.8 to 4.4 cm in length, feed from
the outer edges of leaves inward. Stalks, ears, and silks may also
be attacked if infestation is severe.

E. Insects that feed in the heads of sorghum.

Caterpillars - These soft-bodied, moth larvae have
three pairs of legs near the head and either four or five
pairs of fleshy prolegs.

Corn earworm -
See section C.1. of this key
for larval description. This caterpillar bores deep into the
sorghum seed head, feeding on seed contents and flower stems. It is
usually no longer than 45 mm.

Sorghum webworm -
Feeding on grain, this hairy larva is green with four reddish-tan stripes
and reaches a length of 14 mm. It has four pairs of prolegs, three pairs of
abdominal prolegs and one pair of anal prolegs. It webs
flowers and seeds together.

Sorghum midge maggot -
This tiny maggot, no longer than 2 mm and pink to orange in color, feeds
inside sorghum kernels. The orange adult is similar to a mosquito.